Subgenomic clones previously obtained from a cosmid clone of a new human oncogene, designated dbl for diffuse B cell lymphoma, have been utilized in order to detect the expression of this newly isolated oncogene in fresh human tumors and tumor cell lines. For this screening, a cDNA clone (representing an incomplete copy of the dbl message) obtained from a cDNA library constructed from NIH/3T3 cells in RNAs transfected with the dbl clone, has also been used. Among about 100 RNA preparations screened, positive hybridization signals have been detected by northern blotting with 10 different preparations of either fresh tumors or cell lines. The positive samples included cell lines of clear mesodermal origin, such as fibrosarcomas, rhabdo-and leio-myosarcomas. Cell lines and fresh tumor samples derived from Ewing's sarcoma (a type of tumor whose cell of origin is still controversial) were consistently found to be positive. Further characterization of the oncogene has included the screening of the cDNA library obtained from transfected NIH/3T3 cells in order to isolate the 5' missing portions of the dbl gene. Fragments of cDNA coming from this region of the gene have been obtained and will eventually lead to the construction of a full length cDNA clone.